An undercaliber penetrator shell is known from German patent document 2,743,732 which has similar front, intermediate, and rear core elements each having a front face and a rear face and lying in a stack extending along an axis with the front faces of the intermediate and rear elements engaging the rear faces of the respective front and intermediate elements. A high-density main penetrator body engages against and extends axially rearward away from the rear face of the rear body. A casing sleeve engages snugly around the core elements and has a front end generally at the front element and a rear end secured to the main penetrator body. An aerodynamic tip is secured to and extends axially forward from the front end of the sleeve.
Such an inertial-action shell is extremely effective in penetrating laminated or compartment armor. Nonetheless it is not as good against very heavy armor or laminated armor having a particularly heavy outer layer, that is against such armor the above-described stack-core shell does not penetrate as far as a one-piece armor-piercing bullet.
Thus different type of shells must be used against different targets, or a tradeoff must be made between effectiveness against the one type of armor versus against the other armor type.